Photographic transfer processes and compositions for the practice of said processes



E 2 PHOTOGRAPHIC TRANSFER FROG SSES AND COMPOSITIONS FOR THE PRACTICE OF SKID PROCESSES Filed April 21, 1949 Dec. 15, 1953 L ND 662,822 I Su orf lOa pp IO Pho'losensirive Silver Hulide Layer Liquid "Composifion FIG. I

{Sher Supper? Coniqiner INVENTOR Patented Dec. 15, 1953 PHOTOGRAPHIC TRANSFER PROCESSES AND COMPOSITIONS FOR THE PRAC- TICE OF SAID PROCESSES Edwin H. Land, Cambridge, Mass., asslgnor to Polaroid Corporation, Cambridge, Mass., a corporation of Delaware Application April 21, 1949, Serial No. 88,832

27 Claims.

This invention relates to photographic processes wherein a soluble complex, obtained by reaction with the undeveloped silver halide of an exposed photosensitive emulsion, is transferred from said emulsion and the silver thereof is precipitated in another layer to form an image, and to compositions and products useful in the performance of said processes.

One object of the present invention is to provide a novel process wherein a single layerwise application of a processing liquid to the surface of an exposed photosensitive silver halide element develops the latent image therein and causes the formation of a soluble complex with the undeveloped silver halide, said process being characterized by the presence in the applied liqquid of a relatively uniform dispersion of minute particles which act as silver reduction centers and produce an intense and accelerated precipitation of the silver of the soluble complex in so much of the applied liquid composition as remains on the surface of said element.

Another object is the provision of a novel viscous silver halide developer which contains, in suspension, solid minute particles of a substance which is insoluble in said developer, which has no appreciable fogging action when applied in said developer to a silver halide emulsion, and which accelerates the reduction by the reducing agent of such silver-bearing ions as are dissolved in said developer, which silver-bearing ions may be silver ions or ions of a silver-containing complex.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the sevr eral steps and relation and order of one or more of such steps with respect to each of the others, and the product possessing the features, properties and the relation of elements, which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing wherein:

Figure 1 is a diagrammatic enlarged sectional view illustrating the association of elements during one stage of the performance of the novel transfer process of the present invention, the thicknesses of the various materials being exaggerated; and

Fig. 2 is a diagrammatic perspective view with parts broken away of a novel product comprising a container which carries the processing composition of the invention and a, support upon which said composition is spreadable from said container.

The present invention is primarily concerned with the processing of an exposed silver halide emulsion to give directly, and without further exposure, a positive print of the subject matter of a latent image in said emulsion, and particularly with processes wherein the prints are obtained by the development of the emulsion and by the transfer of a portion at least of the silver of the unexposed regions of said emulsion to a suitable silver-receiving layer, the silver, upon precipitation in said receiving layer, producing a visible image.

In the process of the present invention the development of the latent image and the transfer and precipitation of the silver from the undeveloped regions of the silver halide emulsion occur almost concurrently. A liquid composition is so applied to the surface of a photosensitive silver halide element as to be absorbed in part into the emulsion of said element, and this single liquid application develops the penetrated portion of the emulsion and causes the formation of a soluble silver complex with the remaining undeveloped silver halide in the penetrated portion. The liquid composition is best applied in a thin, uniform, relatively viscous layer, for example, by being spread on the emulsion.

The process is characterized :by the inclusion in the thin liquid layer of a suspension of minute particles of a substance which is capable of accelerating and increasing the formation of metallic silver in the liquid and of aggregating the silver thus formed to intensify the resulting image. The particles are present in solid form, being substantially insoluble in the developing composition but are, nevertheless, able to accelerate the reduction by the developing agent in the liquid of silver-bearing ions which, as hereinbefore indicated, may be present in the form of silver ions or in the form of ions of a, soluble silver complex.

While it has heretofore been proposed to employ so-called crystallization nuclei in transfer processes for the purpose of effecting a silver precipitation, these crystallization or precipitation nuclei have in no instance been contained in the processing liquid as it is applied to the photosensitive layer. In one instance the crystallization nuclei have been selected primarily because of their fogging propensity, that is, because they were substances which were capable of promoting the reduction of silver halides without the action of light. Such crystallization nuclei are, by their very nature, limited to use in transfer processes which must be performed in two stages, the development of the latent image taking place prior to the conversion and transfer of the undeveloped silver halide.

One class. of substances particularly suitable as the silver reduction or precipitation initiators of the present invention are the insoluble metallic sulfides, as for example lead sulfide, cadmium sulfide, zinc sulfide, antimony sulfide, nickel sulfide, cobaltous sulfide, indium sulfide and cupric sulfide, and the metallic selenides as, for example, lead selenide and zinc selenide.

To keep the solid particles of the silver-precipitating substance in suspension in the composition, a solid material is preferably dispersed in the developing composition, as by being dissolved therein, to suitably thicken the composition. By thus increasing the viscosity of the composition this material also makes the composition more easy to spread uniformly over a photosensitive elcment. It is evident that upon application of a layer of the composition in its thickened viscous condition to a photosensitive element, the liquid solvent of the composition will permeate into, and be absorbed by, said element and will in part evaporate, thereby increasing the concentration of the thickening agent at the surface of the element and eventually forming a practically solid film of said thickening agent adjacent to said surface. This film, which contains the suspension of the silver precipitation initiator, serves to receive the silver that is precipitated from the soluble silver complex and, since there exists an imagewise distribution of the latter, a print corresponding to the latent image is formed from this silver in the receiving film.

The thickening agent is preferably a film-ion ing colloid capable of producing a self-supporting solid film when the liquid is entirely removed therefrom, and such a film, upon solidification, may be peeled from the negative with the silver image therein.

The viscous liquid composition is best applied to the surface of the photosensitive element by being spread between the photosensitive element and another sheet material such as paper. The

advantages of using the second sheet are manifold. It provides a base for the silver-receiving layer which can be stripped with that layer from the photosensitive element. It provides a protective covering over what would otherwise be an exposed surface of the liquid layer, thereby greatly minimizing oxidation when a developer is used which is prone to aerial oxidation, and its presence keeps the liquid-spreading mechanism dry during the spreading. By selecting for this other sheet material and absorbent material, the removal of the liquid from the processing composition becomes more rapid and the provision of a solid image-receiving film is accelerated.

In a preferred form of the process the liquid composition is first located between the photosensitive silver halide element and another sheet material adjacent the area of the photosensitive element which is to be processed, and in sufficient bulk to carry out the desired processing. The composition is thereafter spread in a thin layer over this area by squeezing it between the photosensitive element and the other sheet material. This is illustrated and described in detail in my copending application Serial No. 7,795 (now Patent No. 2,647,056, issued July 28, 1953).

The viscous liquid composition in its applied condition contains certain ingredients, some of which can be added to the composition during the spreading thereof but which are most simply introduced therein prior to spreading. These ingredients consist of:

(a) A silver halide developing agent;

(b) A substance for forming soluble silver complexes with silver halide, e. g., sodium thicsulfate;

(0) A substance insoluble in the composition, ir-

reducible by the developing agent (a) in the composition and present in solid minute particles which provide silver reduction centers for the accelerated and intensified precipitation of any silver introduced into said composition as a result of the reaction of the silver halide solvent (b) with the unexposed silver halide of the treated emulsion; and

(d) A. thickening agent increasing the viscosity of the composition to the extent necessary to maintain said minute particles of the silver precipitation initiator (c) in suspension.

Additionally the composition may contain other ingredients rendering the developing agent effective to perform its function, such for example as an alkali and sodium sulfite.

The relation of components employed in the performance of one form of the process of the present invention during a stage of said process is illustrated diagrammatically in Fig. 1 wherein: Hi represents a photosensitive element comprising a support [Ga and a photosensitive silver halide emulsion 19b; l2 represents a support or carrier layer for the transfer print which is obtained by the process; and [4 represents a layer of the relatively viscous liquid-processing composition of the invention. Liquid layer l4 may be obtained by spreading the processing agent, for example in the manner disclosed in my copending application Serial No. 7,795, between sheets if! and I2.

The liquid composition may be provided for spreading as a layer i4 between elements If] and I2 by being contained in an elongated rupturable container [6 which, as shown, has a length at least equal to the transverse dimension of the area of photosensitive element If! to which it is to be applied. Container [6 may be attached to one of elements IE] and I2 and, as shown in Fig, 2, is suitably secured to the print-receiving surface of element [2. The container I6 is preferably inexpensive and disposable and so constructed as to be capable of retaining the liquid composition therein for relatively long periods of time without vapor loss or oxidation. One example of a suitable container of this type is formed from a single multilayer sheet of material comprising three laminae. The inner lamina, which provides the inner surface of the container, is formed of a material which is chemically inert to the processing agent and which is impervious to the liquid of the reagent. One class of materials suitable for this purpose, particularly where the processing composition is an alkaline solution, is the polyvinyl acetals, and of the acetals polyvinyl butyral is a preferred species. A composition comprising 60% to 72% by weight of polyvinyl butyral, 10% to 23% by weight of nitrocellulose, and approximately 5% by weight of dibutyl sebacate is satisfactory as the inner lamina. The intermediate lamina is preferably impervious to the vapor of the processing agent and is formed, for example, of a metallic foil such as lead 01' silver foil. The outer or backing lamina is formed of a strong, deformable, relatively inexpensive sheet material such as a kraft paper.

The container I6 is preferably formed by taking the single sheet of three-ply material and folding the same medially at l8, and thereafter securing the end marginal portions and the longitudinal portions 22 of the two folded faces to one another, providing a central space or cavity 25 for containing the processing liquid.

To fill the container it is possible to adhere together the opposite longitudinally extending marginal portions 22 and one of the end marginal portions 20, the container being filled through the other end which is thereafter sealed.

Some of the ingredients contained in the processing composition after application thereof to th silver halide element may be added to the processing liquid as it is spread between elements I0 and 12, being so located on one or both of said elements as to be dissolved by, or otherwise interacted with, the liquid when the latter wets said element or elements.

Photosensitive element 10 is one of the commercially available photosensitive silver halide films, the term films being understood to include paper-backed emulsions. The present composition and process are particularly adapted to improve the results obtained when th higher speed photosensitive silver halide emulsions are used, such as the emulsion of the relatively high 3 speed orthochromatic films, e. g., Eastman Kodak Verichrome film, having an ASA speed rating of 0200 and an ASA exposure index rating in the y ht of 50, and the extremely high speed panchromatic emulsions, e. g., Eastman Kodak Super XX Pan having an ASA speed rating of 0400 and an ASA exposure index rating in the daylight of 00, and Ansco Triple S Pan.

Element 12, in the form shown, comprises a suitable support 12a which may be provided with a surface coating i2?) which supports such of the reagents as are to be dissolved by the liquid composition as it is applied, and which also preferably contains one or mor stabilizing agents for improving the keeping quality of the transfer print. The stabilizing agents are materials which react subsequent to, or during the latter stages of, the silver precipitation to diminish the alkalinity of the layer it and are, for example, metallic salts or mixtures of salts which, in alkaline solution, consume alk-alis by forming relatively insoluble metallic hydroxides with the hydroxyl ions of the alkali solution. The salts of such metals as zinc, cadmium, and lead give sufficiently insoluble hydroxides to function satisfactorily as alkali-consuming agents. The acetates and nitrates of these metals are best. Also useful in this respect are organic compounds which react in alkaline solution to absorb alkali such, for erample, as dimethyl oxalate, ethyl oxalate, dimethyl tartrate and dimethyl malate. Further examples of suitabl stabilizing agents are to be found in my copending applications serial Nos. 726,982 (now Patent No. 2,584,030, issued January 29, 1952); 727,383 issued July 7, 1953) and 37,252 (now Patent No. 2,635,048, issued April 14, 1953). These stabilizing compounds perform the additional function of increasing the density of the resulting image and, in general, give images having deeper brown and grey colors.

The reagents in layer I222 are preferably contained in a suitable vehicle which can be a film of polyvinyl alcohol, methyl cellulose, ethyl cellulose, sodium carboxymethyl cellulose, cellulose (now Patent No. 2,644,756,

Example 1 A processing composition is prepared which comprises:

Water cc. 1860 Sodium carboxymethyl cellulose (Hercules 1362 medium viscosity type) grams 119 Sodium sulfite do 78 Sodium hydroxide do 74.6 Sodium thiosulfate do 14.5 Citric acid do 38.5 Hydroquinone do 52 Chlorobenzotriazole do 1.5

The sodium carboxymethyl cellulose is dissolved first in the water in a mixer at room temperature. Thereafter, the sodium sulfite, sodium hydroxide, sodium thiosulfate and citric acid are added to the solution, the addition being effected in an inert atmosphere of nitrogen. The hydroquinone is then added and the composition is mixed for an hour at approximately room temperature in a nitrogen atmosphere.

To grams of the foregoing composition there is then added 2 cc. of a fresh 1% sodium sulfide solution. After a thorough mixing there is added slowly, drop by drop, a solution comprising:

Water cc 2 Lead acetate gram 0.016 Cadium acetate do 0.011

These additions produce a rich brown, highly dispersed, transparent suspension of sulfide salts.

The composition obtained in this way is then spread, as shown in Fig. 1, in a layer [4 of ap proximately .002-.003 in thickness between the baryta surface of a sheet of baryta paper l2 and the exposed photosensitive silver halide emulsion lllb of a photosensitive film l0. Emulsion lllb is a relatively high speed orthochromatic emulsion like the emulsion of Eastman Kodak Verichrome film, and has a support 10a of a white paper. Elements l0 and 12 are kept superposed for approximately one minute and, at the end of this time, element i2 is stripped from element l0.

Element l2, when stripped, has on its surface a film of the solid residue of layer l4 and this film contains the precipitated silver so that the positive print is formed therein. Because of the absorption and evaporation of the liquid from layer M, the film that is obtained is of the order of a tenth as thick as the original thickness of layer It. The silver image in the film has good color and density and, because the transferred silver is precipitated so closely to the negative, the process gives an image of higher resolving power. It is to be additionally noted that the process provides a finished print at the end of sixty seconds. With very little loss in density and tone, a positive print can be obtained by stripping the sheet I 2 from photosensitive element In less than fifteen seconds after the liquid is spread between elements 10 and 12.

Although a positive image is formed as quickly as fifteen seconds after the spreading of the layer l4 between elements It) and I2, the various strata involved in the image formation remain sufiiciently wet so that precipitation of silver continues for approximately two minutes thereafter with an attendant increase in the density of the shadows of the image. As a result, by controlling the time of imbibition, i. e., the time between the spreading of layer 14 and the separation of elements [0 and [2, a control is had of the contrast of the finished print. For the ordinary outdoor snapshot a separation of elements [0 and I2, approximately one minute after the spreading of the liquid, is recommended.

Exposure of the lamination to light prior to separation of elements It! and [2 has much the same effect on the growth of the positive image as the separation of element l2 from element II). In certain instances it is advantageous to control the contrast and density of the positive print by making such an exposure prior to the separation of the elements. vents any further increase in density while giving the materials of the lamination more chance to dry and the print-receiving film more opportunity to solidify. Where the processing is to be performed in a camera of the type, for example, shown in United States Patent No. 2,435,717 to Land, the exposure of the lamination can be made by opening the rear door through which the positive print is ultimately removed.

Other materials may be substituted for those :7,

used in the foregoing process, and the proportions may be varied to an appreciable extent. For example, the film-forming material in the processing agent, which imparts the desired viscosity to the latter and maintains the silver reducing centers in suspension, may be any of the high molecular weight polymers which are stable to alkalis and which are soluble in aqueous alkaline solutions. For example, such other plastics as hydroxyethyl cellulose and the sodium salts of polymethacrylic acid and polyacrylic acid may be used. Preferably the plastic or other viscosityimparting agent is contained in the composition in sufficient quantities to impart to the composition a viscosity in excess of 1000 centipoises ,1

at a temperature of approximately 24 C. 'The best results are obtained when the viscosities of the composition are of the order of 1000 to 200,000 centipoises at 24 C.

Where the processing composition is to be kept in storage for relatively long periods of time, it is desirable that the film-forming thickening agent in the composition be selected from materials which are relatively inert to alkalis and which, in an alkaline solution of a developing agent, are not reduced by said developing agent and do not lose their viscosity-imparting characteristics. However, in the event the processing composition is to be used immediately or shortly after it is mixed, relatively hydrolyzable materials such as proteins, e. g., gelatin, and carbohydrates, e. g., the starches, can be employed as the film-forming thickening agents. The term "film-forming colloid, as used herein, is understood to be generic to plastics, proteins and carbohydrates which, when dispersed in a liquid layer either in solution or suspension, will form a continuous solid film when the solvent is entirely removed as by evaporation and/or absorption from the layer.

This preliminary exposure pre- Although element I 2 is preferably baryta paper, it or the outer layer thereof, which comes in contact with the developing composition, may be formed of such other materials as, for example, regenerated cellulose, polyvinyl alcohol, sodium alginate, cellulose ethers such as ethyl cellulose or their derivatives such as sodium carboxymethyl cellulose, aluminum carboxymethyl cellulose and hydroxyethyl cellulose, other papers, proteins such as gelatin, carbohydrates such as the starches, gum arabic, and other natural and synthetic resins as well as mixtures of these materials where the same are compatible.

Other developing agents may be used, for example one of the following: p-aminophenol hydrochloride; bromohydroquinone, chlorohydroquinone; diaminophenol hydrochloride; diaminophenol dihydrochloride; toluhydroquinone; monomethyl-p-aminophenol sulfate; and mixtures of monomethyl-p-aminophenol sulfate and hydroquinone.

To form the soluble silver complex such other complex-forming substance as ammonium thiosulfate may be employed.

It is to be noted that the sulfides of lead and cadmium are present in the composition of Example l and are formed as a result of the reaction of soluble acetate salts and a soluble sulfide. By so forming the particles of the sulfide there is obtained a finely divided suspension in which the dimensions of the particles are such that if subjected to a size frequency analysis they will give a size frequency distribution curve with the peak and the mean line of the curve located at a point on the abscissa below a point corresponding to a particle size having a mean diameter of one micron. This type of finely divided suspension gives extremely satisfactory results, although it is also possible to use larger particles formed in a nonprotective environment and then introduced into the viscous developer.

Example 2 To the mixture of water, sodium carboxymethyl cellulose, sodium sulfite, sodium hydroxide, sodium thiosulfate, citric acid, chlorobenzotriazole and hydroquinone of Example 1 there is added 2 cc. of a 1% sodium sulfide solution. After being mixed thoroughly there is added slowly to the mixture a solution comprising:

Water cc 2 Lead acetate gram 0.032

The resulting mixture containing a suspension of lead sulfide is spread in a layer [4 between a photosensitive element [0 and another sheet material I2 in accordance with the process of Example 1.

Example 3 For the 0.032 gram of lead acetate in the composition of Example 2 there is substituted 0.023 gram of cadmium acetate.

Example 4 A composition is formed in accordance with the procedure outlined in Example 1 containing the following ingredients:

9 Metol (methyl p-aminophenol sulfate) grams 0.27 Hydroquinone do 10.9 1% solution of sodium sulfide cc 14 To this dispersion there is added drop by drop, accompanied by agitation of the mixture, a solution consisting of:

Water cc 14 Zinc acetate grarn 0.12

The resulting composition is spread, as described in Example 1, between a photosensitive element l and another element I2 to provide the latter with a positive print.

Other compositions containing other sulfides as precipitation centers were made up by substituting for the 0.12 gram of zinc acetate, in the above example, one of the following compounds in the specified quantity:

Antimony trichloride gram 0.09 Nickel acetate do 9.14 Cobaltous acetate do 0.15 Indium trichloride do 0.086 Cupri'c acetate do 0.12

Each of these compositions when used in the process of Example 1 produced a very satisfactory print having good color and density.

A finely divided dispersion of particles of at least one insoluble metallic selenide also operates to accelerate silver precipitation and. gives transfer prints which are softer and paler and which have lower contrast than the prints obtained from the use of the corresponding sulfides. Compositions containing selenides may be formulated in accordance with any of the previous examples by substituting for the soluble sulfide compound a corresponding soluble selenide in substantially the same quantities. The required amounts of the soluble selenide and of the metallic salt which reacts therewith to give the desired insoluble particles are added to the composition alternately in small portions. An example of a satisfactory soluble selenide is sodium selenide.

To obtain a less alkaline environment for the silver of the positive print and thereby improve the keeping qualities thereof, element [2' is provided with a surface stratum I2 1) containing a suitable. stabilizing agent in accordance with any of the following. Examples 5 to 8 inclusive:

Example 5 A sheet of baryta paper is run througha bath which is kept in contact with the baryta surface for approximately ten seconds, the bath comprising:

Cadmium acetate grams 9 Neutral lead acetate do .3

Zinc nitrate do 18 Water cc 100 Example 6 The baryta-coated surface of a sheet of baryta paper is dipped for one minute ina solution consisting of:

Water cc 100 Ethyl oxamate grams- 10 Example 7 A sheet of barytapaper has applied to the baryta-coated surface thereof a mixture consisting of:

Water n cc 100 10 Arabol (an aqueous solution of gum arabic) grams 1O Dimethyl oxalate do 8 Zinc nitrate do 4 Example 8 A sheet of baryta paper has applied to the baryta-coated surface thereof, by a dip-coating process, a composition consisting of Water cc 100 Lead acetate i grams 7 Cadmium acetate "don--- 5 Zinc acetate do 4 A 50% aqueous solution. of gum arabic cc 15 Dimethyl tartrate grams 80 The solidification of the film in which the positive print is obtained may be expedited by using, as the film-forming material or thickening agent in the layer H of the processing composition, a

plastic which will react with a material on one of elements I0 and I2 to form a less soluble derivative of said plastic. An example of this type of reaction occurs when the element [2, formed as described in Examples 5 and 8, is used with the compositions of any of Examples 1, 2 and 3. The sodium carboxymethyl cellulose is rendered less soluble by reaction with the lead acetate on sheet l2, the lead of the salt entering into a crosslinking reaction with the sodium carboxymethyl cellulose.

A relatively light colored and substantially opaque film may be formed upon solidification of the layer Id of the liquid processing agent by including a suitable white or lightly colored pigment, such as as titanium dioxide, in any of the foregoing processing compositions. The addition of titanium dioxide in quantities equivalent to from 16% to 20% by weight of the composition gives an opaque white film which makes the developed negative underneath the film invisible in reflected light, and which is sufiiciently light in color to serve as a good background for the silver precipitated through the film to the outer surface thereof. A suihcient amount of silver is precipitated by following the teachings of the preceding examples to produce a visible silver image of adequate density on the side of the opaque film remote from the emulsion. In lieu of titanium dioxide, mixtures of titanium dioxide image and to shield the developed negative from view. The use of pigments in this fashion to provide an opaque image-receiving film avoids the need for stripping the film containing the image from the negative.

It is evident from the foregoing that the process of the invention is extremely rapid, and that the dissolution of the undeveloped silver halide takes place almost concurrently with the development of the exposed silver halide. It is accordingly extremely important to avoid any fogging of the photosensitive emulsion and, as a precaution against this possibility, it is desirable in some instances to include in the emulsion or the processing composition an antifogging agent such as the chlorobenzotriazole of the preceding eX- amples.

To form a tougher and more pliable plastic image-receiving film upon solidification of layer [4, a suitable plasticizer for the film-forming plastic of the composition inert to the ingredients of the composition is included in the composition prior to the spreading of the composition in a layer l4. Glycerin is an example of a satisfactory plasticizer for this purpose, and satisfactory compositions containing this plasticizer are compositions otherwise exactly like the compositions of Exaifiples 1 to 4 but having added thereto 15% by weight of glycerin. The glycerin content is not critical and concentrations of glycerin up to 25% give satisfactory results.

The absorption of liquid from layer I4 and, as a consequence, the solidification of the thickening agent in said layer are accelerated by selecting for element i2 a material which is more water absorbent than the baryta-coated surface of a baryta paper. For example, sheet l2 can be an unsized paper to whose surface there is applied a thin coating of a mixture consisting by weight of:

Sodium carboxymethyl cellulose parts 2 Dimethyl tartrate do 1 Glycerin do 1 Water in suflicient quantity to produce a syrupy mass.

The addition to this mixture of barium sulfate Or titanium dioxide or other white pigments in suitable proportions whitens the surface of the sheet. For the sodium carboxymethyl cellulose of the above mixture equivalent amounts of hydroxyethyl cellulose or polyvinyl alcohol may be substituted.

An interesting application of the process of the invention which gives prints of good density and adequate stability, for example, for many types of letter copying, consists in spreading a very thin layer of the liquid composition of any of the preceding examples between a photosensitive element I and ordinary untreated bond paper, the liquid being spread, for example, by a pair of tightly pressed, rubber-surfaced pressure rollers.

Another application of the processes and compositions of the present invention is in connection with the formation of transparencies suitable, for example, for lantern slides. By selecting for element l2 a transparent support such, for example, as a sheet of transparent plastic, a transparency is obtained which can thereafter be laminated in a conventional manner between two glass plates to provide a lantern slide. The transparent plastic may have the surface thereof suitably treated in order to render the same more adherent to the film in which the positive image is formed. One example of a suitable support is a sheet of cellulose acetate which has been subcoated with three layers, the first of which is a layer of cellulose nitrate, the second of which is a layer of a mixture of equal parts of cellulose nitrate and a hydrolyzed polyvinyl acetate which is 65-85% by weight polyvinyl alcohol. Over the second subcoat there is applied a further coating consisting of sodium carboxymethyl cellulose. These three coats are thin, being of the order of thickness ordinarily employed in the subbing art for subcoats.

By using the subcoated cellulose acetate sheet as element l2 in lieu of the baryta paper of Example 1, in accordance with the process of that example, there is obtained a positive transparency. The keeping qualities of the transparency thus formed may be improved by providing on the sheet, for example in the coating of sodium carboxymethyl cellulose, a suitable stabilizing 12 compound of the type hereinabove specifically described.

The element l2, which serves as the support for the transparent print, may also be formed of cellulose acetate in which the stabilizing materials are incorporated as by casting the sheet of cellulose acetate from a solution which in cludes the stabilizing materials as ingredients. Other transparent plastics may be used in lieu of the cellulose acetate.

By film-forming colloid is meant a material which is capable of being spread when suitably dispersed in a liquid medium, either in solution or suspension, to a suificient thickness to provide a self-supporting solid film when the liquid is dried therefrom. Where the printreceiving films of the present invention, obtained by the solidification of liquid layer M, are to be supported on a sheet material such as element [2, it not necessary to have the thickness of the film sufficient to give a self-supporting layer. Where the liquid layer is applied, as by a doctor blade, directly to the photosensitive element l0 without the aid of a second sheet support [2 and the film in which the positive print is formed is thereafter to be directly stripped from the photosensitive element, the thickness of the liquid layer and the concentration of the thickening agent therein are such as will give a selfsupporting film when the liquid is removed from said layer.

By the term insoluble as used herein is meant a material whose solubility in the solvent containing said material at 20 C. is less than one part in 10,000 by weight.

Since certain changes may be made in the foregoing subject matter without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description, or shown in the accompanying drawing, shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. The process of obtaining transfer prints which comprises applying a relatively thin, discrete layer of a liquid processing composition on the surface of a photosensitive silver halide element containing a latent image, said composition, when applied, including a silver halide developer, a silver halide solvent, solid minute particles of a substance insoluble in said composition for accelerating the reduction by said developer of silver-bearing ions in solution in said composition, and a thickening agent increasing the viscosity of said composition sufficiently to keep said particles in suspension, said thickening agent providing a solid film upon the removal of the liquid content of said layer of processing composition, transporting, by absorption, part at least of said composition into the silver halide layer of said element, developing the latent image and forming a soluble complex with undeveloped silver halide in a stratum of the silver halide layer of said element permeated by the liquid of the composition, transporting said soluble complex from said emulsion to the film of said thickening agent remaining on said surface, and rapidly precipitating silver from the solution of said complex to form an image in silver in said film which is the positive of the subject matter of the latent image.

2. The process of obtaining transfer prints which comprises applying a relatively thin, discrete layer of a liquid processing composition on the surface of a photosensitive silver halide ele- 13 ment containing a latent image, said composition, when applied, including a silver halide developer, a silver halide solvent, solid minute particles of a substance insoluble in said composition for accelerating the reduction by said developer of silver-bearing ions in solution in said composition, a thickening agent increasing the viscosity of said composition sufficiently to keep said particles in suspension, and a lightly colored pigment in sufficient quantity to render the solid film formed upon the removal of the liquid from said layer substantially opaque and light in color, transporting, by absorption, part at least of said composition into the silver halide layer of said element, developing the latent image and forming a soluble complex with undeveloped silver halide in a stratum of the silver halide layer of said element permeated by the liquid of the composition, transporting said soluble complex from said emulsion to the substantially opaque film of said thickening agent remaining on said surface, and rapidly precipitating silver from the solution of said complex to form an image in silver in said film which is the positive of the subject matter of said latent image and which is visible from the side of said film remote from the photosensitive element.

3. The process of obtaining transfer prints which comprises applying a relatively thin, discrete layer of a liquid processing composition on the surface of a photosensitive silver halide ele ment containing a latent image, said composition, when applied, including a silver halide developer, a silver halide solvent, solid minute particles of at least one metallic sulfide insoluble in said composition for accelerating the reduction by said developer of silver-bearing ions in solution in said composition, and a filmforming colloid increasing the viscosity of said composition sufiiciently to keep said particles in suspension, transporting, by absorption, part at least of said composition into the silver halide layer of said element, developing the latent image and forming a soluble complex with undeveloped silver halide in a stratum of the silver halide layer of said element permeated by the liquid of the composition, transporting said soluble complex from said emulsion to the film of said 001- loid remaining on said surface, and rapidly precipitating silver from the solution of said com plex to form an image in silver in said film of colloid which is the positive of the subject matter of the latent image.

4. The process of claim 3 in which the filmforming colloid is a film-forming plastic.

5. The process of claim 4 wherein the plastic is a sodium carboxymethyl cellulose.

6. The process of claim 3 wherein a plurality of metallic sulfides are included in the composition.

7. The process of obtaining transfer prints which comprises applying a relatively thin, discrete layer of a liquid processing composition on the surface of a photosensitive silver halide element containing a latent image, said composition, when applied, including a silver halide developer, a silver halide solvent, solid minute particles of at least one metallic sulfide insoluble in said composition for accelerating the reduction of said developer of silver-bearing ions in solution in said composition, and a film-forming colloid increasing the viscosity of said composi tion sufficiently to keep said particles in suspension, transporting, by absorption, part at least of said composition into the silver halide layer of said element, developing the latent image and forming a soluble complex with undeveloped silver halide in a stratum of the silver halide layer of said element permeated by the liquid of the composition, transporting said soluble complex from said emulsion to the film of said colloid remaining on said surface, precipitating silver from the solution of said complex to form an image in silver in said film of colloid which is the positive of the subject matter of the latent image, and removing said film with the silver precipitated therein as a layer from said photosensitive element.

8. The process of obtaining transfer prints which comprises spreading a layer of a liquid processing composition between the surface of a photosensitive silver halide element containing a latent image and another sheet material, said composition, when applied between said element and said other material, including a silver halide developer, a silver halide solvent, solid minute particles of at least one metallic sulfide insoluble in said composition for accelerating the reduction by said developer of silver-bearing ions in solution in said composition, and a film-forming colloid increasing the viscosity of said composition sufficiently to keep said particles in suspension, transporting, by absorption, part at least of said composition into the silver halide layer of said element, developing the latent image and forming a soluble complex with undeveloped silver halide in a stratum of the silver halide layer of said element permeated by the liquid of the composition, transporting said soluble complex from said emulsion to the film of said colloid remaining on said surface, rapidly precipitating silver from the solution of said complex to form an image in silver in said film of colloid which is the positive of the subject matter of the latent image, and removing said film with the silver image therein as a layer from said photosensitive element by stripping said other sheet material with the film adhered thereto from said element.

9. The process of claim 8 in which the other sheet material is a baryta paper.

10. The process of obtaining transfer prints which comprises applying a relatively thin, discrete layer of a liquid processing composition on the surface of a photosensitive silver halide element containing a latent image, said composition, when applied, including a silver halide developer, a silver halide solvent, solid minute particles of at least one metallic selenide insoluble in said composition for accelerating the reduction by said developer of silver-bearing ions in solution in said composition, and a film-forming colloid increasing the viscosity of said composition sufficiently to keep said particles in suspension, transporting, by absorption, part at least of said composition into the silver halide layer by said element, developing the latent image and forming a soluble complex with undeveloped silver halide in a stratum of the silver halide layer of said element permeated by the liquid of the composition, transporting said soluble complex from said emulsion to the film of said colloid remaining on said surface, and rapidly precipitating silver from the solution of said complex to form an image in silver in said film of colloid which is the positive of the subject matter of the latent image.

11. The process of obtaining transfer prints which comprises applying a relatively thin, discrete layer of a liquid processing composition on the surface of a photosensitive silver halide element containing a latent image, said composition, when applied, including a silver halide developer, a silver halide solvent, solid minute particles of at least one metallic selenide insoluble in said composition for accelerating the reduction by said developer of silver-bearing ions in solution in said composition, and a filmforming colloid increasing the viscosity of said composition sufliciently to keep said particles in suspension, transporting, by absorption, part at least of said composition into the silver halide layer of said element, developing the latent image and forming a soluble complex with undeveloped silver halide in a stratum of the silver halide layer of said element permeated by the liquid or" the composition, transporting said soluble complex from said emulsion to the film of said colloid remaining on said surface, precipitating silver from the solution of said complex to form an image in silver in said film of colloid which is the positive of the subject matter of the latent image, and removing said film with the silver precipitated therein as a layer from said photosensitive element.

12. The process of obtaining transfer prints which comprises spreading a layer of a liquid processing composition between the surface of a photosensitive silver halide element containing a latent image and another sheet material, said composition, when applied between said element and said other material, including a silver halide developer, a silver halide solvent, solid minute particles of at least one metallic selcnide insoluble in said composition for accelerating the reduction by said developer of silver-bearing ions in solution in said composition, and a film-tori" ing colloid increasing the viscosity of said composition sufiicicntly to keep said particles in suspension, transporting, by absorption, part at least of said composition into the silver halide layer of said element, developing the latent image and forming a soluble complex with undeveloped silver halide in a stratum of the silver halide layer or" said element permeated by the liquid of the composition, transporting said soluble complex from said emulsion to the film of said colloid remaining on said surface, rapidly precipitating silver from the solution of said complex to form an image in silver in said film of colloid which is the positive of the subject matter of the latent image, and removing said film with the silver image therein as a layer from said photosensitive element by stripping said other sheet material with the 111m adhered thereto from said element.

A liqu d processing composition for forming prints the transfer of components from a silver halide emulsion, said composition comprising a silver halide developer, solid minute particles of a substance substantially insoluble in said composition, said particles constituting reduction centers for accelerating the reduction by said developer of silver-bearing ions in said composition, and a thickening agent increasing the viscosity of the composition suihciently to keep the particles in suspension, said thickening agent providing solid, film-forming residue when the liquid of said composition removed therefrom, said substance being at least one compound from the class consisting of the relatively insoluble metal sulfides and selcnides.

14. A liquid processing composition for forming prints by the transfer of components from a silver halide emulsion, said composition comprising a silver halide developer, a substance for forming soluble silver complexes with silver halide, solid minute particles of a substance substantially insoluble in said composition, said partic es constituting reduction centers for accelerating the reduction by said developer of silverbearing ions in said composition, and a thickening agent increasing the viscosity of the composition sufiiciently to keep said particles in suspension, said thickening agent providing a solid, film-forming residue when the liquid of said composition is removed therefrom, said substance being at least one compound from the class consisting of the relatively insoluble metal sulfides and selenides.

15. A liquid processing composition for forming prints by the transfer of components from a silver halide emulsion, said composition comprising a silver halide developer, a substance for forming soluble silver complexes with silver halide, solid minute particles of at least one metal sulfide substantially insoluble in said composition, said particles constituting reduction centers for accelerating the reduction by said developer of silver-bearing ions in said composition, and a thickening agent increasing the viscosity of the composition surficiently to keep said particles in suspension, said thickening agent providing a solid, film-forming residue when the liquid of composition is removed therefrom.

15. A liquid processing composition for forming prints by the transfer of components from a silver halide emulsion, said composition comprising a si'rv halide developer, a substance for iorming soluble silver complexes with silver halidc, solid minute particles of a mixture of at least tu'o metal sulfides substantially insoluble in said co iposition, said particles constituting reduccenters for accelerating the reduction by said developer of silver-bearing ions in said compositron, and a thickening agent increasing the viscosity of the composition sufliciently to keep said particles in suspension, said thickening agent prov ding a solid, film-forming residue when the liquid of said composition is removed therefrom. 17. A liquid processing composition for forming prints by the transfer of components from a silver halide emulsion, said composition comprising a silver halide developer, a substance for forming soluble silver complexes with silver halide solid minute particles of zinc sulfide, said particles constituting reduction centers for accelerating the reduction by said developer of silver-bearing ions in said composition, and a thick cning agent increasing the viscosity of the composit on sufficiently to keep said particles in suspension, said thickening agent providing a solid, him-forming residue when the liquid of said composition is removed therefrom.

18. A liquid processing composition for formzngprints by the transfer of components from a si ver halide emulsion, said composition comprising a silver halide developer, a substance for orming soluble silver complexes with silver halide, solid minute particles of cadmium sulfide said particles constituting reduction centers for accelerating the reduction by said developer of silver-bearing ions in said composition, and a thicken ing agent increasing the viscosity of the COIIlpOSllllOl'l sufficiently to keep said particles in suspension, said thickening agent providing a solid, film-forming residue when the liquid of said composition is removed therefrom.

19. liquid processing composition for forme prints by the transfer of components from a silver halide emulsion, said composition comprising a silver halide developer, a substance for forming soluble silver complexes with silver halide, solid minute particles of lead sulfide, said particles constituting reduction centers for accelcrating the reduction by said developer of silverbearing ions in said composition, and a thickening agent increasing the viscosity of the composition suiiiciently to keep said particles in suspension, said thickening agent providing a solid, filmforming residue when the liquid of said composition is removed therefrom.

20. A liquid processing composition for forming prints by the transfer of components from a silver halide emulsion, said composition comprising a silver halide developer, a substance for forming soluble silver complexes with silver halide, solid minute particles of at least one metal sulfide substantially insoluble in said composition, said particles constituting reduction centers for accelerating the reduction by said developer of silverbearing ions in said composition, and a filmforming organic colloid increasing the viscosity of the composition sufilciently to keep said particles in suspension.

21. A liquid processing composition for forming prints by the transfer of components from a silver halide emulsion, said composition comprising a, silver halide developer, a substance for forming soluble silver complexes with silver halide, solid minute particles of at least one metal sulfide substantially insoluble in said composition, said particles constituting reduction centers for accelerating the reduction by said developer of silver-bearing ions in said composition, and a film-forming plastic increasing the viscosity of the composition sufiiciently to keep said particles in suspension.

22. A liquid processing composition for forming prints by the transfer of components from a silver halide emulsion, said composition comprising hydroquinone, sodium thiosulfate, solid minute particles of a metal sulfide substantially insoluble in and irreducible by said composition, a film-forming plastic increasing the viscosity of the composition sufficiently to keep said particles in suspension, and an alkali metal hydroxide.

23. A liquid processing composition for forming prints by the transfer of components from a silver halide emulsion, said composition comprising hydroquinone, sodium thiosulfate, solid minute particles of lead sulfide substantially insoluble in and irreducible by said composition, a film-forming 18 plastic increasing the viscosity of the composition sufficiently to keep said particles in suspension, and an alkali metal hydroxide.

24. A liquid processing composition for forming prints by the transfer of components from a silver halide emulsion, said composition comprising hydroquinone, sodium thiosulfate, solid minute particles of a metal sulfide substantially insoluble in and irreducible by said composition, a sodium carboxymethyl cellulose plastic increasing the viscosity of the composition sufliciently to keep said particles in suspension, and an alkali metal hydroxide.

25. The liquid processing composition of claim 13 wherein said substance is at least one metal selenide.

26. The processing composition of claim 25 wherein said substance is a mixture of at least two metal selenides.

27. The processing composition of claim 14 wherein the said substance is at least one metal selenide and said thickening agent is a filmforming plastic.

EDWIN H. LAND.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,279,276 Crabtree Sept. 17, 1918 2,121,397 Downing June 21, 1938 2,317,750 Fermazin Apr. 27, 1939 2,323,246 Schneider et al. June 29, 1943 2,532,014 Rott June 20, 1944 FOREIGN PATENTS Number Country Date 761,428 France Oct. 6, 1931 53,311 France Jan. 22, 1941 (Addition to No. 879,995) 879,995 France Mar. 5, 1942 53,513 France July 16, 1945 (Addition to No. 873,507) 59,365 Netherlands Apr. 17, 1947 470,855 Great Britain Aug. 23, 1937 OTHER REFERENCES Mees: The Theory of the Photographic ProcesS, PD. 456-457, 462-463, 305-309, 315-318, 568, 570-571; Macmillan 00., N. Y., 1942.

Varden: PSA Journal, vol. 13, September 1947, pp. 551-555. 

1. THE PROCESS OF OBTAINING TRANSFER PRINTS WHICH COMPRISES APPLYING A RELATIVELY THIN, DISCRETE LAYER OF A LIQUID PROCESSING COMPOSITION ON THE SURFACE OF A PHOTOSENSITIVE SILVER HALIDE ELEMENT CONTAINING A LATENT IMAGE, SAID COMPOSITION, WHEN APPLIED, INCLUDING A SILVER HALIDE DEVELOPER, A SILVER HALIDE SOLVENT, SOLID MINUTE PARTICLES OF A SUBSTANCE INSOLUBLE IN SAID COMPOSITION FOR ACCELERATING THE REDUCTION BY SAID DEVELOPER OF SILVER-BEARING IONS IN SOLUTION IN SAID COMPOSITION, AND A THICKENING AGENT INCREASING THE VISCOSITY OF SAID COMPOSITION SUFFICIENTLY TO KEEP SAID PARTICLES IN SUSPENSION, SAID THICKENING AGENT PROVIDING A SOLID FILM UPON THE REMOVAL OF THE LIQUID CONTENT OF SAID LAYER OF PROCESSING COMPOSITION, TRANSPORTING, BY ABSORPTION, PART AT LEAST ONE SAID COMPOSITION INTO THE SILVER HALIDE LAYER OF SAID ELEMENT, DEVELOPING THE LATENT IMAGE AND FORMING A SOLUBLE COMPLEX WITH UNDEVELOPED SILVER HALIDE IN A STRATUM OF THE SILVER HALIDE LAYER OF SAID ELEMENT PERMEATED BY THE LIQUID OF THE COMPOSITON, TRANSPORTING SAID SOLUBLE COMPLEX FROM SAID EMULSION TO THE FILM OF SAID THICKENING AGENT REMAINING ON SAID SURFACE, AND RAPIDLY PRECIPITATING SILVER FROM THE SOLUTION OF SAID COMPLEX TO FORM AN IMAGE IN SILVER IN SAID FILM WHICH IS THE POSITIVE OF THE SUBJECT MATTER OF THE LATENT IMAGE.
 13. A LIQUID PROCESSING COMPOSITION FOR FORMING PRINTS BY THE TRANSFER OF COMPONENTS FROM A SILVER HALIDE EMULSION, SAID COMPOSITION COMPRISING A SILVER HALIDE DEVELOPER, SOLID MINUTE PARTICLES OF A SUBSTANCE SUBSTANTIALLY INSOLUBLE IN SAID COMPOSITION, SAID PARTICLES CONSTITUTING REDUCTION CENTERS FOR ACCELERATING THE REDUCTION BY SAID DEVELOPER OF SILVER-BEARING IONS IN SAID COMPOSITION, AND A THICKENING AGENT INCREASING THE VISCOSITY OF THE COMPOSITION SUFFICIENTLY TO KEEP THE PARTICLES IN SUSPENSION, SAID THICKENING AGENT PROVIDING A SOLID, FILM-FORMING RESIDUE WHEN THE LIQUID OF SAID COMPOSITION IS REMOVED THEREFROM, SAID SUBSTANCE BEING AT LEAST ONE COMPOUND FROM THE CLASS CONSISTING OF THE RELATIVELY INSOLUBLE METAL SULFIDES AND SELENIDES. 